We had a Shih-tzu that we rescued years ago that had this....and like you, we felt sorry for him, that is way we got him too.
Anyway....the vet tried sooo many treatments...one was some sort of cattle treatment that was very potent. It was so many years ago...I am sorry I can not remember all the names of the meds the vet tried. I know one started w/ an "I".
I believe he said this was passed from the mother. I had a lot of research on it at the time, but have since tossed it all (I guess). We put Buddy to sleep after two years............(he would have been 4).....
Not just because of the mange, but vairous other health issues this poor guy had.
Good luck
